On Saturday, Mr Rajoy said he was triggering Article 155 of the constitution - an unprecedented move - which allows for direct rule to be imposed in a crisis on any of the country's autonomous regions.

But Catalan leaders say they will not accept the plan.

Speaking to BBC Radio 4's Today programme, foreign affairs spokesman Raul Romeva said: "How can the European Union live with that situation [if this happens]?

"Because what I can tell you is that the people and the institutions in Catalonia will not let this happen."

He said the Spanish government needed to recognise that the people of the region had voted for independence.

Mr Rajoy insisted the measures would not mean Catalan self-government itself was being suspended and that they were intended to remove the people who had taken illegal action.

The country's Deputy Prime Minister, Soraya Sáenz de Santamaría, told Spanish radio Onda Cero (in Spanish) that Catalan leaders were "completely not in compliance with the constitution and the statute of autonomy".

Once the Senate approves Article 155, Mr Puigdemont will stop receiving a salary and will not be able to carry out his functions, she added.

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Media captionCatalan police caught in a political crisis

Catalonia's far-left CUP party - a key support for Mr Puigdemont's minority government in the regional parliament - has warned of a campaign of "massive civil disobedience" if Madrid imposes direct rule on the region.

Spanish media report that the Catalan leader is planning to present his arguments to a commission of the Spanish Senate on Wednesday, but this has yet to be confirmed.

There have been calls by Mr Puigdemont's supporters to declare a snap election before direct rule becomes effective.